This invention relates to an actuator assembly for a vehicle brake. Specifically, this invention relates to an improved fastener arrangement for a brake actuator of the wedge type and, more specifically, to an improved fastener arrangement for a wedge type brake actuator for use with an air brake system for a heavy duty truck application.
Heavy duty truck air brake systems typically are of the drum type in which the brake actuator basically comprises a lever member which is secured to the piston rod of the air motor by means of a clevis. Increasingly, however, wedge type actuators are finding application in heavy duty truck air brake systems. These wedge type actuators are typically employed in a disc brake environment, as in the present disclosure, but they may also be used in a drum brake environment. In either environment, the manner in which the piston rod of the air motor is fastened to the wedge actuator becomes critical. Specifically, in the case of lever type actuators, the attachment of the threaded piston rod of the standard air motor to the actuator is readily accomplished by the use of a clevis including a threaded bore into which the rod is secured (e.g., see FIG. 1 of U.S. Pat. No. 4,094,390). The brake supplier typically provides the actuator assembly, less air motor, to the original equipment manufacturer (OEM) who then fastens the air motor to the actuator as a part of the vehicle assembly process. In the case of a wedge type actuator, however, it is important that the actuator assembly, once assembled by the supplier, not be opened up to allow contaminants to enter the critical interface between the wedge actuator and the tappet member driven by the wedge. Prior art wedge actuator designs have either required that the OEM open up the actuator assembly to accomplish the attachment of the standard threaded piston rod to the wedge actuator, or have required that the piston rod of the air motor be customized in a manner to facilitate its attachment to the wedge actuator. The prior art designs requiring the OEM to open up the actuator assembly to accomplish the attachment are undesirable since the potential for contaminates entering the wedge interface area during the attachment process is quite high. The prior art designs requiring a customized piston rod are undesirable in that they require the OEM, as well as the various field service organizations, to inventory separate air motors for lever type actuators and wedge type actuators. Alternatively, the suppliers providing a wedge actuator requiring a customized piston rod may choose to themselves assemble the air motor to the actuator assembly and deliver the completed assembly to the OEM. This alternative precludes contamination of the wedge interface, since the actuator need not be opened up by the OEM, and simplifies the inventory requirement of the OEM, since the air motor, although customized, is provided by the brake supplier. However, this alternative detracts from the brake assembly flexibility of the OEM, and fails to address the inventory problems of the field service organizations.